1. Field of the Invention
The present invention relates to a bearing unit supporting a rotation shaft rotatably, or supporting a rotation body rotatably to a shaft, and a motor and electronic equipment, both equipped with the bearing unit.
2. Description of Related Art
As a bearing unit supporting a rotation shaft rotatably, a bearing unit constituted as shown in FIG. 19 is conventionally known.
A bearing unit 100 shown in FIG. 19 is one supporting a rotation shaft 101 rotatably, and is equipped with a radial bearing 104 for supporting the rotation shaft 101 in its peripheral rotation direction, and a housing 105 housing the radial bearing 104.
In the bearing unit 100, the radial bearing 104 constitutes a fluid dynamic bearing together with a lubricating oil being a viscous fluid filled in the housing 105, and dynamic pressure generation grooves 111 for generating a dynamic pressure are formed on an inner peripheral surface, in which the rotation shaft 101 is inserted.
As shown in FIG. 19, the housing 105 having accommodated therein the radial bearing 104 supporting the rotation shaft 101 has a shape accommodating the radial bearing 104 shaped in a cylinder in a manner surrounding the radial bearing 104, and the housing 105 is a member formed by molding a synthetic resin integrally.
The housing 105 is composed of a housing main body 106 shaped in a cylinder and a bottom sealing portion 107 constituting one end side portion formed integrally with the housing main body 106 for sealing the end side of the housing main body 106. On the opened other end side of the housing main body 106, an upper sealing portion 108 is provided. The housing 105 and the upper sealing portion 108 are integrated to be one body by means of a method such as heat welding or ultrasonic welding.
A shaft insertion hole 109, through which the rotation shaft 101 supported rotatably by the radial bearing 104 housed in the housing 105 is inserted, is formed at the central part of the upper sealing portion 108. A thrust bearing 110 for rotatably supporting a bearing supporting portion 102 is integrally formed at the central part on an inner surface side of the bottom sealing portion 107. The bearing supporting portion 102 is formed at one end of the rotation shaft 101, which is supported by the radial bearing 104, in a thrust direction.
The thrust bearing 110 is formed as a pivot bearing supporting the bearing supporting portion 102 of the rotation shaft 101 at a point. The bearing supporting portion 102 is formed in an arc or a tapered tip.
A slip-out preventing member 115, such as a washer, is provided between the bearing supporting portion 102 and a shaft main body 103. The slip-out preventing member 115 prevents the rotation shaft 101 from slipping out of the housing 105. The slip-out preventing member 115 is made of polyoxymethylene (POM), polyslider, nylon or the like.
Now, the shaft insertion hole 109 is formed to have an inner diameter larger than the outer shape of the shaft main body 103 in some degree in order that the rotation shaft 101 inserted into the shaft insertion hole 109 may rotate without contacting with an inner peripheral surface of the shaft insertion hole 109 slidably. In this case, the shaft insertion hole 109 is formed to have a gap 112 of a space x5 sufficient for preventing leakage of a lubricating oil 113 filled in the housing between the inner peripheral surface of the shaft insertion hole 109 and an outer peripheral surface of the shaft main body 103 from the inside of the housing 105.
A tapered portion 114 is formed on an outer peripheral surface of the rotation shaft 101 opposed to the inner peripheral surface of the shaft insertion hole 109. The tapered portion 114 inclines in a manner of enlarging the gap 112 formed between the outer peripheral surface of the rotation shaft 101 and the inner peripheral surface of the shaft insertion hole 109 toward the outside of the housing 105. The tapered portion 114 forms a pressure gradient in the gap 112 formed between the outer peripheral surface of the rotation shaft 101 and the inner peripheral surface of the shaft insertion hole 109, and a force draws the lubricating oil 113 filled in the housing 105 into the inside of the housing 105. Because the lubricating oil 113 is drawn in the inside of the housing 105 at the rotation of the rotation shaft 101, the lubricating oil 113 surely permeates the dynamic pressure generation grooves 111 of the radial bearing 104 made as a fluid dynamic bearing to generate a dynamic pressure. Thereby, stable support of the rotation shaft 101 is realized, and leakage of the lubricating oil 113 filled in the housing 105 can be prevented.
The bearing unit 100 configured as shown in FIG. 19 exposes the rotation shaft 101 only at one end on the side of the shaft insertion hole 109, and covers the whole bearing unit 100 by the housing member seamlessly except for a small gap of the shaft insertion hole 109. Consequently, the bearing unit 100 can prevent leakage of the lubricating oil 113 to the outside of the housing 105. Moreover, because the communicating portion to the outside is only the gap of the shaft insertion hole 109, scattering of the lubricating oil due to an impact can be prevented. Furthermore, the bearing unit 100 can prevent the rotation shaft 101 from falling off from the housing 105 by the slip-out preventing member 115.
However, because the above-mentioned bearing unit 100 is configured to surround the circumference of the bearing main body by means of two parts of the housing 105 and the upper sealing portion 108, there is the possibility that lubricating oil can ooze out from a joint portion of the housing 105 and the upper sealing portion 108.
In another case, a bearing unit has the housing thereof integrally formed by means of a molded body of a synthetic resin for preventing the oozing of the lubricating oil from the joint portion of the housing.
As shown in FIG. 20, the rotation shaft 101 is inserted into the radial bearing 104, and the slip-out preventing member 115 is attached to the side of the bearing supporting portion 102 of the inserted rotation shaft 101 in this bearing unit. Then, a space forming member 116 is attached to the side of the bearing supporting portion 102 of the radial bearing 104, and thereby the bearing unit is temporarily assembled.
Next, the temporarily assembled rotation shaft 101, the radial bearing 104 and the space forming member 116 are attached to a die. Then, as shown in FIG. 21, any one of the above-mentioned synthetic resins is outsert molded on the outer circumferences of the temporary assembled rotation shaft 101, the radial bearing 104 and the space forming member 116 to form a housing 117.
After the formation of the housing 117, the lubricating oil 113 is filled in the housing 117 to form a bearing unit 120 shown in FIG. 22.
However, in the above-mentioned bearing unit 120, the thickness of a sealing portion forming member 118 of the die is limited as shown in FIG. 21. That is to say, there is the possibility that the space x5 of the gap 112 of the bearing unit 120 formed by means of the die becomes too large, and the lubricating oil 113 leaks from the gap 112 to make it impossible to obtain good rotation performance.
Moreover, the temperature of the die at the time of the outsert molding of the housing 117 shown in FIG. 21 is 60-100° C., and the temperature of the resin is 200° C. The heat of the molding temperature conducts to the slipout preventing member 115 through the radial bearing 104 and the space forming member 116, and consequently the temperature of the slip-out preventing member 115 is raised to about 120° C. There is the possibility of the thermal deformation of the slip-out preventing member 115 owing to the rise of the temperature.
The sizes of the slip-out preventing member 115 are determined in order to form a gap x3 between the space forming member 116 and the slip-out preventing member 115 and a gap x4 between the slip-out preventing member 115 and the shaft 110 for keeping the rotation performance of the shaft. In the aforementioned deformed slip-out preventing member 115 owing to the temperature rise, the gaps x3 and x4 provided for keeping the rotation performance are changed to cause a defect in rotation by a contact of the slip-out preventing member 115 with the rotation shaft. Consequently, there is the possibility that good rotation performance cannot be obtained.
Moreover, as a variation of the above-mentioned bearing unit 120, there is a method of performing the outsert molding of the housing without inserting the shaft at the step of temporary assembly, and then of inserting the rotation shaft after molding. In this bearing unit, it is possible to adjust the space x5 of the gap 112 to be a suitable magnitude, but a defect in which the rotation shaft cannot be inserted owing to a deformation of the slip-out preventing member 115 caused by the temperature at the outsert molding and consequently the bearing unit cannot be assembled in a suitable state, or the like is generated.
[Patent Document 1]
    Japanese Patent Application Publication (KOKAI) No. 2003-130043